Enhancing Extension Recommendations for Improving Herbicide Resistance Management on Georgia Roadsides

The presence of Italian ryegrass on Georgia roadsides reduces motorist site visibility and increases maintenance costs for the DOT. Herbicide selection is limited on roadsides due to economics and the susceptibility of roadside turfgrasses to injury. Consequently, agronomists often apply the same chemistries every year without rotating herbicide modes of action. These spray programs promote the development of herbicide resistance in weed populations and may compromise the safety and sustainability of roadsides throughout Georgia. Research was conducted to evaluate the extent of herbicide resistance to glyphosate and acetolactate synthase (ALS)-inhibitors in areas it is most commonly found on Georgia roadsides. These are the two chemistries that have been primarily used for controlling ryegrass on roadsides for several decades. Twenty-eight populations were sampled on routes that had sprayed herbicides for ryegrass control in the winters of 2018 and 2019. Plants that were not controlled by the current programs were grown in the greenhouse, seed was harvested, and new plants were screened for resistance. In dose response, experiments approximately one-third of the ryegrass plants exhibited resistance or enhanced tolerance levels to glyphosate compared to known susceptible populations and the majority of other plants collected on roadsides. In hydroponic assays, approximately 20% of the ryegrass populations were resistant to ALS-inhibitor herbicides. Glyphosate-resistant ryegrass was controlled by Envoy (clethodim) and Piper (flumioxazin + pyroxasulfone) when applied alone or in combinations with Esplanade (indaziflam). The majority of the ryegrass sampled in roadsides was susceptible to glyphosate and ALS-inhibitors. Nonetheless, resistance was detected in several populations that could warrant rotation to other chemistries to help delay the spread of these biotypes on roadsides.


  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Figures; Photos; References; Tables;
  • Pagination: 37p

Subject/Index Terms

Filing Info

  • Accession Number: 01745916
  • Record Type: Publication
  • Report/Paper Numbers: FHWA-GA-20-1710, 17-10, GEORGIA DOT RESEARCH PROJECT 17-10
  • Created Date: Jul 22 2020 3:49PM